The National Security Agency violated privacy protections between 2006 and 2009 when it collected phone records from millions of Americans by failing to meet court-ordered standards, U.S. officials told the Wall Street Journal Tuesday:

The revelations called into question NSA's ability to run the sweeping domestic surveillance programs it introduced more than a decade ago in the wake of the 2001 terrorist attacks. Officials said the violations were inadvertent, because NSA officials didn't understand their own phone-records collection program.

"There was nobody at the NSA who had a full understanding of how the program worked,'' said an intelligence official.

Top U.S. officials, including NSA Director Keith Alexander, have repeatedly reassured lawmakers and the public that the phone-records program has been carefully executed under oversight from the secret Foreign Intelligence Surveillance Court court.

James Clapper, the Director of National Intelligence, released a statement on new unclassified documents revealing the violations of privacy here.